In particular, Sues often have perfect traits on the edge of unrealism: unfailing beauty, exceptional charisma, sustained strength and/or ability. In addition, Sues also have boo-hoo tragic pasts, including but not limited to: entire family being murdered at a young age, being disrespected and/or unwanted for a majority of early life, slavery, etc etc etc. Yet somehow, they are able to function well and pull through the misery.
In conclusion, Sues are horribly written, horribly read self-insert characters with unrealistic traits, even for fanfiction. Although some Sues can be well-written and therefore pleasing, most suck. Never read one and certainly never write one. For the male counterpart, see Stu.
Harry Potter's parents have been murdered at birth giving him a physically impossible scar on his majestic forehead, despite rejection at an early age he has managed to become a big hero.
Bella Swan has...oh, don't even make me MENTION her.
When someone "sues" another, it is usually done by somebody with a huge ego and greedy intentions.
Although it can help our society and solve problems amongst ourselves, too many people abuse this power. In the end, it becomes more childish then a kid throwing a temper tantrum in a toy store.
Betty sued the coffee house because she is an idiot.
Peggy sue, peggy sue.
Pretty, pretty, pretty, pretty peggy sue.
Oh, peggy, my peggy sue.
Well, I love you girl.
Yes, I need you, peggy sue